Astable multivibrator pulse generator



, Sept. 1969 D. A. SCHULTZ 3,465,263

ASTABLE MULTIVIBRATOR PULSE GENERATOR Filed Jan. 26, 1967 1 N VENTOR.

DONALD A. SCHULZTZ United States Patent A free-running multivibrator wherein one of the crosscoupling capacitors has been replaced by a battery which serves the dual function of energizing one of the tubes and coupling the output of this tube to the input of the other tube.

This circuit is claimed to be and intended to be that of a very low frequency multivibrator or pulse-generator. It is a hybrid circuit intended to have less or a minimum of low frequency attenuation within-the-circuit. It is simultaneously and in fact, a tone generator when used with a suitable audio amplifier with loudspeaker. It has musical quality and the tones may be adjusted to standard musical pitch notes by selection of proper resistors for this, if so desired. The connections and components shown in the circuit diagram and described in this paper are intended and there are no omissions in the basic diagram submitted herewith.

In the circuit diagram provided, the symbols numbered 1, 2, 3 and 4 represent any quantity of individual fixed resistors which are connected between the control grid of triode number and separate switch contacts of selector switch number 7. Number 8 represents the rotor of selector switch which is manually operated and used to select and ground any one resistance connected to its contacts. The rotor is shown connected to resistor number 1, grounding that resistor. The respective resistors should differ in ohmic amount between the extreme values of 1500 ohms and 15 megohms. The 1500 ohm resistor will produce the higher note with the balance of the circuit and the 15 megohm resistor will produce the lowest lowest pulse rate when it is connected into the circuit. These resistors when connected between the grid of triode number 15 and chassis or ground (B) will serve to discharge condenser number 11 at a rate approximately determined by the time-constant of condenser number 11 and the grounded resistor connected to it. Push-buttons or toggle switches may be substituted for switch number 7 to facilitate selection of tones or pulse rates in sequence or at random at the option of the operator.

Triodes numbers 15 and 16 are assumed identical, that is, in type number and condition and filament voltage rating. Filament type tubes are shown in the diagram but cathode-type tubes may be used as the cathodes may be properly grounded. Battery number 13 is the filament battery or a proper filament transformer may be substituted if cathode-type tubes are used. Battery number 14 is the plate supply for triode number 16. This is conventional, except the plate potential need not exceed 15 volts. It is not critical. Battery number 12 functions as the anode battery for triode number 15. It is connected with the polarity shown. It is also very low in voltage. In practice, with this circuit, no advantage is gained from using a battery voltage in excess of three volts in this part of the circuit.

The grid of triode number 16 is connected to the junction of the negative end of this battery and the ungrounded end of resistor number 5. This part of the circuit is so-designed as to eliminate one condenser and one resistor of the conventional R-C amplifier stage. Therefore, the voltage drop which occurs across common resis- 3,465,263 Patented Sept. 2, 1969 tor number 5 with any anode current through triode number 15 will appear as a negative bias at the grid of triode number 16. This functions so as to block or cut-off the anode current of triode number 16 during the duty-cycle of the oscillator. The dynamic blocking of triode number 16 causes the plate potential to rise periodically at point 18. This causes condenser number 11 to regularly charge toward a positive supply potential thru the resistor which is connected into the circuit by switch number 7 and through the plate load resistor number 6 (15,000 ohms). Triode number 15 becomes more conductive, until the condenser is no longer charging, then triode number 15 becomes less conductive, the grid bias on triode number 16 becomes less negative and this tube draws current at a steady or slightly decreasing rate for a comparatively long interval before the next blocking pulse occurs. This duty-cycle re-occurs automatically at a rate determined mostly by the RC combination connected to the grid of triode number 15.

Any pair of medium gain triodes of the same type may be used if they are reasonably matched, in good condition, and provided with the proper filament voltage and connected as shown by the wiring diagrammed. Twin triode type 19, a two-volt tube, was used with success.

Switch contacts shown blank at number 9 and number 10 could be connected respectively to a continuously variable resistance of the range 1500 to 15 megohms or one or more contacts could be connected to a sensor or more so as to indicate or report temperature variation, humidity variation, or light variation. The sensor should be of the type which varies its resistance with the temperature, humidity, light or other quantity being measured or reported.

Proper operation of the circuit is evidenced by a popping sound or buzz or tone or whistle depending upon the circuit constants being used. Condenser number 11 may be about microfarad; resistor number 5 must be about 9000 ohms. This is somewhat critical. Condenser number 11 may be removed from the circuit and another capacitor of neighboring value substituted for it to change to a different range of audible notes or pulse rates. A larger capacity used at this point will cause lower notes or slower pulse rates to be produced; smaller capacities introduced at this point will cause higher notes or tones to be produced when the selector switch number 7 is switched through its gamut of ditferent resistors. That is, condenser number 11 functions as a range and feedback condenser.

This circuit, when connected as shown, oscillates independently of other tubes, circuits, or contrivances. It is self-sustaining, starts easily, and requires no adjustment to remain stable in operation. Transition from one pulserate or tone to another is smooth and reliable. No sync signal or driving signal is required but a synchronizing voltage could be introduced by connecting a small condenser to point number 20 and supplying a sync signal to that point.

The circuit operates normally at a low audio level and to be audible, requires the input of a two-stage audio amplifier with loudspeaker to be connected between points number 18 and chassis-ground (point number 17). The circuit may be observed in operation by connecting a sensitive milli-ammeter between resistor number 6 and battery number 14. The circuit is functioning normally when the plate current is fairly large and steady with a regular dip occurring at each pulse.

The circuit is stable. It was designed to fill the gap in multivibrators which may become inoperative at less than 10 cycles per second. Cathode resistors are not required in this basic circuit. It will pulse as few as three pulses per minute. That is it will function normally in a large region below 10 cycles per second as well as 10 cycles per second and higher.

If one desires an output signal from the oscillator other than obtained by connecting an ampifier between point number 18 and number 17, one may connect between points numbers 17 and 19 or between points numbers 17 and 20. This will yield a pulse of different amplitude or phase.

One side of the circuit is considered as ground or common. This is the wire common to triode number 15, triode number 16, battery number 13, battery number 14, switch number 7 and resistor number 5. This wire may be connected to a metal chassis but need not be connected to a metal chassis.

All of the symbols in the circuit represent electronic or radio components familiar to many and not difficult to procure. The components should be wired together as shown. No transformer or more than one fixed capacitor are intended in the basic circuit. Both triodes are grounded cathode amplifiers coupled by two diiferent methods of coupling in a loop so that the circuit is oscillatory. More capacitors may be added at the input or the output of the circuit for the addition of other circuits. The dark connecting lines in the diagram represent wiring between the components.

What is claimed is:

1. A free-running multivibrator comprising first and second active elements, each having a control electrode, an output electrode, and a common electrode; said common electrodes being connected together; energizing and resistive means connected between said output and common electrodes of said second active element; first and second resistive means connecting respectively said control and common electrodes of said first and second active elements; a condenser coupling said output electrode of said second active element to said control electrode of said first active element; and a battery coupling said output electrode of said first active element to said input electrode of said second active element; whereby said battery serves to energize said first active element and to couple the output thereof to said second active element.

References Cited UNITED STATES PATENTS 3,253,234 5/1966 Kretzmer 331144 X FOREIGN PATENTS 1,112,106 8/ 1961 Germany.

ROY LAKE, Primary Examiner S. H. GRIMM, Assistant Examiner U.S. Cl. X.R. 33l177 

